1. Field of the Invention
The present invention relates to apparatus and methods for connecting tubular materials to construct various articulated products such as furniture, shelving, small buildings and the like. More particularly, the invention pertains to apparatus and methods for joining a plurality of tubular materials such as metal electrical conduit or pipe to fabricate various articulated structures and frameworks therefor.
2. State of the Art
As a horticulturist, I have sought to create a portable greenhouse and associated products which are lightweight, weather-resistant, strong, and which are easily and quickly assembled (and taken apart) by the average adult from readily obtained and/or inexpensive materials.
Currently, lightweight greenhouse structures which are considered to be lightweight may be formed by several methods. Typically, construction involves the cutting, bending and welding of steel or aluminum pipe into frameworks or sections which may be assembled into a desired structural framework. The framework is typically covered with a variety of materials, such as thin plastic and/or aluminum sheeting or film. Where a structure is designed to be periodically dis-assembled and stored, pipe fittings are used which involve screwing/unscrewing of pipe sections, or removal of fasteners from each fitting. However, conventional pipe fittings and pipe used to make the frame members are relatively expensive, and the time and expense in welding/brazing pipe fittings onto the pipe are also appreciable. Inasmuch as iron and steel pipe rust quickly, galvanized or stainless steel pipe may be used, but are much more expensive. If galvanized pipe is used, welding or brazing results in generation of toxic zinc fumes, and the high temperature produces local de-galvanization, rendering the pipe subject to oxidation. Aluminum pipe is relatively expensive, and stainless steels are too expensive for general use in this application. Furthermore, the commercial fittings for joining pipe and tubing lack sufficient strength for this application, often being formed of white metal or aluminum. In the latter case, use of both aluminum and ferrous metal in the same structure will result in severe electrochemical corrosion, as is well known.
This inventor tried for many years to find or create joints/connectors for interconnecting conventional pipe and tubing into structures. Galvanized electrical conduit is a very attractive material for forming structures, inasmuch as it is (1) resistant to oxidation, (2) very lightweight, (3) strong, (4) easy to use, and (5) inexpensive. Furthermore, galvanized conduit is readily available in a variety of sizes, including nominal ½ inch, ¾ inch, 1 inch, 1½ inch, and 2 inch sizes, and larger. However, the commercially available connectors for joining conduit have insufficient rigidity and strength for effectively forming free-standing articulated structures therefrom.
An example of a conventional pipe connector is shown in U.S. Pat. No. 3,921,360 to Baldwin. The connector is shown as an irregular polyhedron with 12 surface structures and screw-threaded receivers for eight threaded struts. The device has a complex internal structure, requires repeated threading operations. Furthermore, parallel struts are not achievable with this connector.
In U.S. Pat. No. 4,925,330 to Cornish, a six-way connector is described which has surfaces to which structural elements may be attached by four screws apiece. The structural elements are of a complex construction and must be provided with ends which match the connector ends. Use with ordinary tubular materials is not in view. The thin walls of the connector appear to be subject to bending under relatively mild loading.
U.S. Pat. No. 5,556,219 to Mason shows a connector comprising a hemispherical member with a plurality of non-circular projections having a post. A flexible tubular member with precisely formed holes may be placed over a projection and squeezed to compress the member, permitting sliding the member over the post until it enters one of the holes.
In U.S. Pat. No. 6,032,430 to Soukup, up to six elongate bars are held in annular sleeves, and the sleeve ends compressed in an array to hold them in place.
U.S. Pat. No. 6,108,984 to Davidson teaches the connection of up to six struts of a geodesic dome in a connector having cylindrical fingers extending from a central member. The fingers and tubes have matching machined ends whereby a tube may be inserted in a finger and rotated for retention therein. The system is complex and requires special machining.
In U.S. Pat. No. 5,273,633 to Husson et al., an assembly node is shown which comprises two half-dome portions with holes for insertion of tubular elements therein. Bolts are passed through holes in the tubular elements and screwed to the assembly node to hold the elements in place.
U.S. Pat. No. 6,413,004 to Lin describes a tube connector which comprises a six-way connector with tubular ends having slits and projecting retaining members. A tube having a small opening near its end may be passed over a tubular end until the projecting retaining member snaps into the small tube opening to retain it in place. The connector is complex to form and is limited in angular adaptability.
A primary object of the present invention is to make available a system for joining a plurality of common tubular materials in a manner which is simple, for easy and quick assembly/disassembly of an almost limitless range of useful apparatus. It is also an object to make available such a system which is lockable, capable of carrying heavy loads without bending or breaking, and resistant to deterioration.